Ms Mills dispensed with barristers for an appearance at the High Court last week and on Wednesday during applications to keep Sir Paul out of her home and to gain access to his.

It is believed that Ms Mills, who has retained the services of London law firm Mishcon de Reya in the main divorce battle over money and custody of three-year-old daughter Beatrice, is trying to keep her legal costs down. Barristers can charge upwards of £15,000 a day.

Her final legal bill could already top £1 million, although she is likely to receive at least £20 million and as much as £100 million. Sir Paul has an estimated £825 million fortune.

When Ms Mills brought her own action in the High Court last week she was photographed clutching an A4 note pad containing scribbled notes. The notes formed the basis of her speech and were headed: “I’m seeking an order for occupation of the matrimonial home. The decision on her application to have Sir Paul, 64, kept out of her home in Hove, East Sussex, is expected soon.

The case is being heard by Mrs Justice Baron, one of the most eminent law judges in the country. Ms Mills is being advised on most aspects of the case by Anthony Julius, who handled the divorce of Diana, Princess of Wales.

A source close to Ms Mills said last night: “In certain aspects of this matter Heather has dispensed with barristers and has been representing herself.

“She has been working very closely with her law firm but felt that she could manage without recourse to barristers. She is conscious of legal bills.”

Sir Paul, 64, and his wife announced in May that they were to end their four-year marriage.

Ms Mills recently said she would rather have had all her limbs cut off than face the criticism she got for her relationship with the ex-Beatle.

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